In the past, in a CMOS (Complementary Metal Oxide Semiconductor) image sensor, when readout transistors for reading out pixel signals are turned off, a negative voltage VRL generated by a charge pump is input in the gates of the readout transistors via readout-control signal lines TR (0 to m: m is an identifier for identifying each readout row) in order to increase pixel characteristics. In other words, since all the pixel-signal readout transistors except for the readout row are turned off, the negative voltage VRL is input in almost all the readout-control signal lines.
Meanwhile, since the control signal lines in which the negative voltage VRL is input are wired above the pixels physically, the control signal lines have coupling components with vertical transfer lines VSL (0 to n: n is an identifier for identifying each vertical transfer line VSL) and floating diffusions FD (0 to i: i is an identifier for identifying each floating diffusion FD). As a result, variation components of the negative voltage VRL deteriorate pixel data of the vertical transfer lines VSL (0 to n) via the vertical transfer lines VSL (0 to n) and the floating diffusions FD (0 to i).
For example, even according to a correlated-double-sampling signal processing, it is difficult to remove noise components due to variations of negative voltages and offset components between samples. Therefore noises remain in AD (Analog/Digital)-converted pixel signals, and the quality of a captured image is deteriorated as a result (see Patent Documents 1 and 2).
Further, there are two kinds of variation components of the negative voltage VRL, i.e., noises generated by a charge pump itself and variations due to coupling and driving pixels.
Some technologies are proposed to solve one of them, i.e., noises generated by a charge pump itself (see Patent Documents 3 and 4).
Meanwhile, there is known a method of increasing a negative voltage capacitor to reduce variations due to coupling and driving pixels.
Patent Document 1: Japanese Patent Application Laid-open No. 2000-152082
Patent Document 2: Japanese Patent Application Laid-open No. 2005-323331
Patent Document 3: Japanese Patent Application Laid-open No. 2003-348822
Patent Document 4: Japanese Patent Application Laid-open No. 2008-042305